<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript">
        function updateStyle(){
            let ele = document.querySelector("span")
            ele.style.color="black";
        }
    </script>
</head>
<body>
<div>
    <span style="color: red; font-size: 30px; background-color: aqua">这是修改样式</span>
</div>
<button onclick="updateStyle()">点击修改样式</button>
</body>
</html>